The present invention relates to a capacitor for semiconductor memory device and a method of manufacturing the same, and more particularly to a capacitor for semiconductor memory device capable of increasing the storage capacitance as well as preventing leakage current and a method of manufacturing the same.
As the number of memory cells composing DRAM semiconductor device has been recently increased, occupancy dimension of each memory cell is gradually decreased. Meanwhile, capacitors formed in the respective memory cells require a sufficient capacitance for precise reading out of storage data. Accordingly, the current DRAM semiconductor device requires memory cells in which capacitors having larger capacitance as well as occupying small area is formed. The capacitance of a capacitor can be increased by using an insulator having high dielectric constant as a dielectric layer, or by enlarging the surface area of a lower electrode. In a highly integrated DRAM semiconductor device, a Ta2O5 layer having a higher dielectric constant than that of the nitride-oxide(NO) is now used as a dielectric, thereby forming a lower electrode of a 3-Dimentional structure.
FIG. 1 is a cross-sectional view showing a capacitor for conventional semiconductor memory device. Referring to FIG. 1, a gate electrode 13 including a gate insulating layer 12 at a lower portion thereof is formed according to a known technique on the upper part of a semiconductor substrate 10 which a field oxide layer 11 is formed at a selected portion thereof. A junction region 14 is formed on the semiconductor substrate 10 at both sides of the gate electrode 13, thereby forming an MOS transistor. A first interlevel insulating layer 16 and a second interlevel insulating layer 18 are formed on the upper part of the semiconductor substrate 10 in which the MOS transistor is formed. A storage node contact hole h is formed inside the first and the second interlevel insulating layers 16,18 so that a junction region 14 is exposed. A cylinder type lower electrode 20 is formed according to a known method, inside the storage node contact hole h so as to be in contact with the exposed junction region 14. A HSG(hemi-spherical grain) layer 21 is formed on a surface of a lower electrode 20 to increase the surface area of the lower electrode 20 more. Afterwards, a rapid thermal nitridation(RTN) process is performed on the surface of the lower electrode 20 which the HSG layer 21 is formed thereon by ex situ to prevent generation of a natural oxidation layer. Next, a first Ta2O5 layer is formed on an upper part of the lower electrode 20 that is treated by the RTN process at temperature of approximately 400xcx9c450xc2x0 C. to the thickness of 53xcx9c57 xc3x85. Afterwards, an annealing step is performed at a low temperature, and then a second Ta2O5 layer is formed to the same process and same thickness as those of the first Ta2O5 layer. Sequentially, annealing steps at low and high temperatures are performed in series, thereby forming the Ta2O5 layer 23. Afterwards, to crystallize the Ta2O5 layer 23, the layer 23 is thermal-treated again at a selected temperature. An upper electrode 25 is formed of a polysilicon layer or metal layer doped on the Ta2O5 layer 23 and made of a doped polysilicon layer or a metal layer.
However, a difference in the composition rate of Ta and O is occurred since the Ta2O5 layer 23 generally has unstable stoichiometry. As a result, substitutional Ta atoms, i.e. vacancy atoms are generated in a thin film. Since those vacancy atoms are oxygen vacancies, leakage current is occurred.
Now, the Ta2O5 layer is oxidized so as to remove the substitutional Ta atoms therein in order to stabilize the unstable stoichiometry thereof. However, the following problems are caused when the Ta2O5 layer is oxidized to prevent leakage current. That is, the Ta2O5 layer has great oxidation reactivity with the lower and the upper electrodes formed of polysilicon or TiN. Accordingly, during the oxidation process for oxidizing the substitutional Ta atoms, an oxide layer having low dielectric constant is formed at an interface by reaction between the Ta2O5 layer and the lower electrode or the upper electrode. And, oxygen moves to the interface between the Ta2O5 layer and the lower electrode, thereby deteriorating homogeneity in the interface.
Further, due to the reaction between an organic substance such as Ta(OC2H5)5 used as a precursor and O2(or N2O) gas, impurities such as carbon atoms C, carbon compounds(CH4, C2H4) and H2O are generated in the Ta2O5 layer. Those impurities increase leakage current in the capacitor and deteriorate the dielectric characteristics of the Ta2O5 layer. Accordingly, a capacitor of great capacitance is difficult to obtain.
Moreover, the method using the Ta2O5 layer as a dielectric layer requires an extra ex-situ process before the formation of the Ta2O5 layer and after the cleaning step. Also, the Ta2O5 layer should be deposited in double steps and two thermal processes at low and high temperatures should be performed after the deposition. Therefore, manufacturing process is cumbersome.
Accordingly, it is one object of the present invention to provide a capacitor for semiconductor device with a dielectric layer having low leakage current and high dielectric constant.
Furthermore, the other object of the present invention is to provide a method of manufacturing a capacitor for semiconductor device capable of simplifying manufacturing process thereof.
To achieve the foregoing objectives, the present invention according to one aspect includes: a lower electrode; a dielectric layer formed on the lower electrode; and an upper electrode formed on the dielectric layer, wherein the dielectric layer is a TiON layer.
Further, the present invention according to another aspect provides a method of manufacturing the capacitor of a semiconductor memory device including the steps of: forming a lower electrode on a semiconductor substrate; depositing a TiON layer as a dielectric layer on the lower electrode; and forming an upper electrode on the TiON layer.
The present invention according to still another aspect provides a method of manufacturing the capacitor of a semiconductor memory device including the steps of: forming a lower electrode on a semiconductor substrate; surface-treating to prevent a natural oxide layer from generating on the surface of the lower electrode; depositing a TiON layer on the lower electrode using an organic Ti metal precursor; thermal-treating the TiON layer; and forming an upper electrode on the TiON layer, wherein the TiON layer is formed by chemical vapor reaction of Ti chemical vapor, NH3 gas and O2 gas in the LPCVD chamber maintained at temperature of 300 to 600xc2x0 C., wherein the Ti chemical vapor is an evaporated organic Ti metal precursor.